docs: def entrance_angled(angle, method='Idelchik'):
      r'''Returns loss coefficient for a sharp, angled entrance to a pipe
      flush with the wall of a reservoir. First published in [2]_, it has been
      recommended in [3]_ as well as in [1]_.
  
      .. math::
          K = 0.57 + 0.30\cos(\theta) + 0.20\cos(\theta)^2
  
      .. figure:: fittings/entrance_mounted_at_an_angle.png
         :scale: 30 %
         :alt: entrace mounted at an angle; after [1]_
  
      Parameters
      ----------
      angle : float
          Angle of inclination (90° = straight, 0° = parallel to pipe wall),
          [degrees]
      method : str, optional
          The method to use; only 'Idelchik' is supported
  
      Returns
      -------
      K : float
          Loss coefficient [-]
  
      Notes
      -----
      Not reliable for angles under 20 degrees.
      Loss coefficient is the same for an upward or downward angled inlet.
  
      Examples
      --------
      >>> entrance_angled(30)
      0.9798076211353315
  
      References
      ----------
      .. [1] Rennels, Donald C., and Hobart M. Hudson. Pipe Flow: A Practical
         and Comprehensive Guide. 1st edition. Hoboken, N.J: Wiley, 2012.
      .. [2] Idel’chik, I. E. Handbook of Hydraulic Resistance: Coefficients of 
         Local Resistance and of Friction (Spravochnik Po Gidravlicheskim 
         Soprotivleniyam, Koeffitsienty Mestnykh Soprotivlenii i Soprotivleniya
         Treniya). National technical information Service, 1966.
      .. [3] Blevins, Robert D. Applied Fluid Dynamics Handbook. New York, N.Y.: 
         Van Nostrand Reinhold Co., 1984.
      '''
      if method is None:
           method = 'Idelchik'
      if method == 'Idelchik':
          cos_term = cos(radians(angle))
          return 0.57 + cos_term*(0.2*cos_term + 0.3)
      else:
          raise ValueError('Specified method not recognized; methods are %s'
                           %(entrance_angled_methods))